Contaminated sediments typically contain complex mixtures of organic and inorganic chemicals at concentrations several orders of magnitude greater than in overlying water. Most of the information regarding fate and effects of contaminants in aquatic systems is based on aqueous exposure. Research on sediment contaminants has only recently received attention and therefore our understanding of the mechanisms that influence fate and effects of sediment-sorbed chemicals is relatively primitive. This proposed research will investigate toxicity and bioaccumulation of a mixture of seven sediment contaminants (trichlorethylene, lead, benzene, chloroform, phenol, chromium, and arsenic) in several species of invertebrates and fish. Acute and chronic toxicity tests will be conducted by exposing organisms to either bulk laboratory-spiked sediments or interstitial water extracted from these sediments. Uptake and depuration will be measured in chironomids (Chironomus riparius) and pharmacokinetic models will be developed to describe bioaccumulation of these sediment contaminants. The transfer of sediment contaminants through a simple laboratory food chain (sediments to Chironomus riparius to Lepomis macrochirus) will be documented and the relative importance of dietary versus aqueous exposure to these contaminants will be determined. Since chironomids are the dominant prey of juvenile bluegill in nature, results obtained from these experiments will be applicable to bluegill populations foraging in natural systems with contaminated sediments.